MATLAB: Mu law expander error

Question

i have sawtooth function when i expanded the function using this function

i get error

my code

 T = 10*(1/50);
Fs = 10000; 
dt = 1/Fs;
t = 0:dt:T-dt; 
x4 = sawtooth(2*pi*50*t);
u=255
expander = ((-1 + (1+u)^abs(Y)) ./ u);

Answer 1

   T = 10*(1/50);
  Fs = 10000; 
  dt = 1/Fs;
  t = 0:dt:T-dt; 
  x4 = sawtooth(2*pi*50*t);
  u=255
  expander = ((-1 + (1+u).^abs(x4)) ./ u);